Experiment 17: Determining a Rate Law and Rate Constant Chemistry 1250 William Michael Lawless TA – Heewon J. Choi Experiment Completed: 11/5/2013 Report Turned In: 11/12/2013 Purpose: The purpose of this lab is to learn and understand the differences in the 1st, 2nd, and zero rate laws. Over a period of time, measurements were taken to find the rate. These measurements will be used in the rate law in order to find the rate constant. Procedure: Please refer to the General Chemistry 1250 Lab Manual, 2013, Department of Chemistry, The Ohio State University, Experiment 17, Pages 199-‐121, for the proper procedure in this experiment. Data: See attached report sheet, as well as the printed data tables for the data collected during this experiment. Sample Calculations: See attached hand-‐written sample calculations sheet. Results and Discussion During the lab, the reaction was tracked by taking a large amount of absorbance readings. From the absorbance readings after boiling the solution, the Beer’s law graph could be plotted. From the Beer’s Law graph, I found that the slope was 197.12. This slope value was used as eb to calculate the [CrEDTA-‐]t value, which is equal to A/eb. From the calculated [CrEDTA-‐]t values, I was able to calculate [Cr3+]t as well. [Cr3+]t is equal to the [CrEDTA-‐]t final – [CrEDTA-‐]t. The [Cr3+]t values for each solution were plotted on the y-‐axis and the time was plotted on the x-‐axis for the zero order rate law. The first order rate law graph was obtained by plotting the natural log of [Cr3+]t on the y-‐axis and the time on the x-‐axis. Finally, the second order rate law was plotted by using 1/[Cr3+]t on the y-‐axis and time on the x-‐axis. From these graphs, the objective was to determine which order this reaction was. The graph with the most parallel slopes is stated to be the order of the reaction. Based on my data and graphs, this reaction is a first-‐order reaction. From this information, I was about to use the first-‐order rate law in order to find the rate constant. The average rate constant was 0.0114s-‐1 with 0.0007 average deviation. The conclusion that this is a first order reaction is reasonable because the rate constants and slope match the molarity of the solutions. Many errors could have been made in this experiment. A possible determinate error in this experiment could have been the initial mixing of the solution. If the correct solutions were not mixed, the entire experiment would have large error. Also, this experiment called for taking many readings. Our time could have been off which would have created error in the absorbance readings. We also may have read the wrong cuvette a few times. This experiment called for very precise readings and any error could cause larger error in the overall data. Conclusion: The overall purpose for this lab was to use absorption readings in order to determine what order the reaction was and calculate the rate constant. From this reaction, it was clear that it was a first order reaction. From this knowledge, the rate constant for the reaction could be determined. I learned from this experiment that different reactions occur at different speeds and determining the rate constant can tell what speed they react at. Solution 1: Time (min) A [CrEDTA-‐]t [Cr3+]t ln[Cr3+]t 1/[Cr3+]t 0 0.069 0.000350 0.00305 -‐5.79 328 5 0.094 0.000477 0.00292 -‐5.84 342 10 0.157 0.000796 0.00260 -‐5.95 384 15 0.191 0.000969 0.00243 -‐6.02 411 20 0.2 0.001015 0.00239 -‐6.04 419 25 0.238 0.001207 0.00219 -‐6.12 456 30 0.268 0.001360 0.00204 -‐6.19 490 35 0.29 0.001471 0.00193 -‐6.25 518 40 0.315 0.001598 0.00180 -‐6.32 555 45 0.335 0.001699 0.00170 -‐6.38 588 50 0.359 0.001821 0.00158 -‐6.45 633 55 0.371 0.001882 0.00152 -‐6.49 659 60 0.389 0.001973 0.00143 -‐6.55 701 65 0.405 0.002055 0.00135 -‐6.61 743 70 0.419 0.002126 0.00127 -‐6.67 785 75 0.431 0.002186 0.00121 -‐6.71 824 Solution 2: [CrEDTA-‐]t [Cr3+]t ln[Cr3+]t 1/[Cr3+]t Time (min) A 0 0.069 0.000350 0.00333 -‐5.70 300 5 0.090 0.000457 0.00322 -‐5.74 310 10 0.120 0.000609 0.00307 -‐5.79 326 15 0.154 0.000781 0.00290 -‐5.84 345 20 0.188 0.000954 0.00273 -‐5.90 367 25 0.228 0.001157 0.00252 -‐5.98 396 30 0.255 0.001294 0.00239 -‐6.04 419 35 0.285 0.001446 0.00223 -‐6.10 448 40 0.310 0.001573 0.00211 -‐6.16 475 45 0.341 0.001730 0.00195 -‐6.24 513 50 0.357 0.001811 0.00187 -‐6.28 535 55 0.378 0.001918 0.00176 -‐6.34 567 60 0.400 0.002029 0.00165 -‐6.41 606 65 0.421 0.002136 0.00154 -‐6.47 648 70 0.427 0.002166 0.00151 -‐6.49 661 75 0.450 0.002283 0.00140 -‐6.57 716 Solution 3: [CrEDTA-‐]t [Cr3+]t ln[Cr3+]t 1/[Cr3+]t Time(min) A 0 0.065 0.000330 0.00375 -‐5.59 267 5 0.083 0.000421 0.00366 -‐5.61 273 10 0.117 0.000594 0.00349 -‐5.66 287 15 0.150 0.000761 0.00332 -‐5.71 301 20 0.182 0.000923 0.00316 -‐5.76 317 25 0.221 0.001121 0.00296 -‐5.82 338 30 0.250 0.001268 0.00281 -‐5.87 356 35 0.281 0.001426 0.00265 -‐5.93 377 40 0.306 0.001552 0.00253 -‐5.98 396 45 0.334 0.001694 0.00239 -‐6.04 419 50 0.378 0.001918 0.00216 -‐6.14 462 55 0.392 0.001989 0.00209 -‐6.17 478 60 0.401 0.002034 0.00205 -‐6.19 489 65 0.418 0.002121 0.00196 -‐6.24 510 70 0.432 0.002192 0.00189 -‐6.27 530 75 0.459 0.002329 0.00175 -‐6.35 571 Solution 4: Time (min) 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 A [CrEDTA-‐]t [Cr3+]t ln[Cr3+]t 1/[Cr3+]t 0.09 0.000457 0.00377 -‐5.58 265 0.094 0.000477 0.00375 -‐5.59 266 0.120 0.000609 0.00362 -‐5.62 276 0.168 0.000852 0.00338 -‐5.69 296 0.199 0.001010 0.00322 -‐5.74 311 0.238 0.001207 0.00302 -‐5.80 331 0.274 0.001390 0.00284 -‐5.86 352 0.304 0.001542 0.00269 -‐5.92 372 0.333 0.001689 0.00254 -‐5.98 394 0.365 0.001852 0.00238 -‐6.04 420 0.383 0.001943 0.00229 -‐6.08 437 0.406 0.002060 0.00217 -‐6.13 461 0.428 0.002171 0.00206 -‐6.19 486 0.449 0.002278 0.00195 -‐6.24 512 0.468 0.002374 0.00186 -‐6.29 539 0.490 0.002486 0.00174 -‐6.35 573
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